使用微服务Spring Cloud集成Kafka实现异步通信（消费者）
1、本文架构
本文目标是使用微服务Spring Cloud集成Kafka实现异步通信。其中Kafka Server部署在Ubuntu虚拟机上，微服务部署在Windows 11系统上，Kafka Producer微服务和Kafka Consumer微服务分别注册到Eureka注册中心。Kafka Producer和Kafka Consumer之间通过Kafka Server实现异步通信。
出于便于测试的目的，我通过浏览器触发Kafka Producer发送消息，观察Kafka Consumer的后台是否打印出接收到的消息内容。
Ubuntu 上部署Kafka Server，详见博文：Ubuntu下Kafka安装及使用-CSDN博客
Eureka注册中心的搭建过程和完整代码，详见博文：微服务1：搭建微服务注册中心（命令行简易版，不使用IDE）-CSDN博客
Kafka Producer微服务的完整代码，详见博文：使用微服务Spring Cloud集成Kafka实现异步通信-CSDN博客
本文的重点是实现下图中的深蓝色部分：Kafka Consumer微服务。
2、创建Spring boot项目（Kafka Consumer微服务项目）：
mvn archetype:generate -DgroupId=com.test -DartifactId=microservice-kafka-consumer -DarchetypeArtifactId=maven-archetype-quickstart
项目代码的完整目录如下图所示：
编辑pom.xml，添加依赖包：
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-stream-binder-kafka</artifactId>
</dependency>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.test</groupId><artifactId>microservice-kafka-consumer</artifactId><packaging>jar</packaging><version>1.0-SNAPSHOT</version><name>microservice-kafka-consumer</name><url>http://maven.apache.org</url><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.3.0.RELEASE</version><relativePath/> </parent><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-netflix-eureka-client</artifactId></dependency> <dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>3.8.1</version><scope>test</scope></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-stream-binder-kafka</artifactId></dependency></dependencies><dependencyManagement><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-dependencies</artifactId><version>Hoxton.SR4</version><type>pom</type><scope>import</scope></dependency> </dependencies></dependencyManagement><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build></project>
编辑application.yml，配置kafka消费者：
consumer:
#消费的主题
topic: test-topic
#消费者组id
group-id: test-group
#是否自动提交偏移量
enable-auto-commit: true
#提交偏移量的间隔-毫秒
auto-commit-ms: 1000
#客户端消费的会话超时时间-毫秒
session-timeout-ms: 10000
#实现DeSerializer接口的反序列化类键
key-deserializer: org.apache.kafka.common.serialization.StringDeserializer
#实现DeSerializer接口的反序列化类值
value-deserializer: org.apache.kafka.common.serialization.StringDeserializer
server:port: 8030
spring:application:name: microservice-kafka-consumerkafka:bootstrap-servers: 192.168.23.131:9092consumer:group-id: test-groupenable-auto-commit: trueauto-commit-ms: 1000session-timeout-ms: 10000key-deserializer: org.apache.kafka.common.serialization.StringDeserializervalue-deserializer: org.apache.kafka.common.serialization.StringDeserializereureka:client:serviceUrl:defaultZone: http://localhost:8080/eureka/instance:prefer-ip-address: true
App.java的完整代码如下：
package com.test;import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.kafka.annotation.KafkaListener;@SpringBootApplication
@EnableDiscoveryClient
public class App
{@KafkaListener(topics = "mydemo1")public void listen(String msg) throws Exception {System.out.println( "-----> Recv a msg: " + msg );}public static void main( String[] args ){System.out.println( "Hello World!" );SpringApplication.run(App.class, args);}
}
3、测试
在浏览器输入，触发Kafka Producer向Kafka Server发送消息：
http://localhost:8020/kafka/sendMsg?msg=测试消息testmsg在Kafka Consumer的后台打印出收到的消息：
